1. Field of the Invention
The present invention relates to a structure of a liquid crystal display (LCD) panel and a method for its manufacture. In particular, the invention relates to a structure of an ODF (One-Drop-Fill) LCD panel and a method for its manufacture.
2. Related Technology
In the conventional method for manufacturing a liquid crystal display panel, an empty cavity comprised of two opposed and mutually aligned substrates attached by a sealing member is formed. The cavity is then filled with liquid crystal through a vacuum insertion method. However, the conventional method has various disadvantages, especially in the case of a large-size liquid crystal display panel. In particular, the conventional method is time consuming and requires a large amount of liquid crystal material to completely fill the cavity. For these reasons, a faster fill technique known as a “one-drop fill” (ODF) technique has been developed to reduce the time and cost of manufacturing. A version of the ODF method is disclosed in U.S. Pat. No. 5,263,888, issued to Teruhisa Ishihara et al. on Nov. 23, 1993, the entirety of which is incorporated herein by reference for its teachings regarding the ODF method. The basic concepts of the ODF method are illustrated in FIGS. 1a and 1b. FIG. 1a is a view showing an array substrate 9 of a conventional ODF-LCD panel, and FIG. 1b is a perspective view showing a pair of substrates of a conventional ODF-LCD panel comprising the array substrate 9 and a color filter substrate 1. The array substrate 9 has a sealing member 7 formed at a peripheral region surrounding a display region in which drops 8 of liquid crystal are provided. The drops may include a small amount of solid spherical spacers, e.g. 0.3 wt %. The color filter substrate 1 has a color pixel area 3 at its center and a black matrix area 5 at its periphery. The array substrate 9 and the color filter substrate 1 are held spaced apart and placed in a vacuum chamber of a vacuum assembly apparatus. While still under atmospheric pressure, the color filter substrate 1 is positioned precisely above the array substrate 9. Air pressure in the vacuum chamber is then reduced, and the two substrates are brought together so that the color filter substrate 1 becomes superposed on the array substrate 9. The sealing member 7 is then hardened, e.g. by application of ultraviolet radiation.
The main challenge of the conventional ODF method is controlling the total volume of the liquid crystal drops. If the total volume of the liquid crystal drops is insufficient to fill the LCD panel, bubbles of empty space (“vacuum bubbles”) are formed within the panel. This problem can be overcome by providing a greater volume of liquid crystal drops on the substrate. However, if the total volume of liquid crystal is excessive or insufficient, as a result of either overfilling or underfilling, the gap between the two substrates will not be uniform and the device will not accurately reproduce images. Environmental factors such as temperature changes or dropping of the device may also produce these problems.
An improved version of the ODF method that is intended to overcome these problems is described in issued Taiwanese patent No. 482,913. In this method, a frame-shaped bulge is formed on a substrate between a sealing member and a display region. The liquid crystal is dropped inside the display region surrounded by the frame-shaped bulge on the substrate, wherein the volume of liquid crystal is greater than the volume of the display region surrounded by the frame-shaped bulge and less than the volume of a region surrounded by the sealing member. The substrate is then superposed to another substrate, and excess liquid crystal flows through a break into a buffer region formed between the sealing member and the frame-shaped bulge. While this method can overcome the problems of insufficient liquid crystal, the method has other disadvantages. One disadvantage is that it is difficult for the liquid crystal to flow through the break into the buffer region. Another difficulty is that bubbles are still caused by insufficient liquid crystal in the buffer region, and those bubbles enter the display region while the LCD panel is shaken.